Anomalous dispersion glass

ABSTRACT

An anomalous dispersion glass having an Abbe&#39;&#39;s number ( Nu d) of 58-68 and a partial dispersion ratio (Phg) of 0.4425-0.4650, produced by adding 0.3-7.0 wt. parts of CeO2 and 0-2 wt. parts of Sb2O3 to 100 wt. parts of phosphate glass which is composed of P2O5 40-70 wt. percent, B2O3 1-21 wt. percent, Al2O3 1-8 wt. percent, B2O3+Al2O3 2-24 wt. percent, BaO 8-42 wt. percent, ZnO 0-9 wt. percent, MgO 0-7 wt. percent, CaO 0-7 wt. percent, SrO 011 wt. percent, La2O3 0-7 wt. percent, where BaO+MgO+ZnO+SrO+CaO+La2O3 are 15-52 wt. percent.

United States Patent [1 1 Izumitani et al.

[ Jan. 15, 1974 ANOMALOUS DISPERSION GLASS [75] Inventors: Tetsuro Izumitani; Isao Masuda,

both of Tokyo, Japan [73] Assignee: Hoya Glass Works, Ltd.,

Shinjuku-ku, Tokyo, Japan [22] Filed: May 19, 1972 [2]] Appl. No.: 254,965

[30] Foreign Application Priority Data May 2|, I971 Japan 46-34546 [52] US. Cl. 106/47 Q [51] Int. Cl. C036 3/16 [58] Field of Search 106/47 Q, 47 R [56] References Cited UNITED STATES PATENTS 2,996,39l 8/1961 Weissenberg et al l06/47 0 3,711,264 l/l973 Robinson et al 106/47 Q FOREIGN PATENTS OR APPLICATIONS I,O89,935 9/l960 Germany 106/47 Q Phg OTHER PUBLICATIONS Schroeder, H.,Oxide Layers Deposited from Organic Solutions in Physics of Thin Films edited by Hass et al. 1969, Vol. 5 pg. 137.

Primary Examiner-Helen M. McCarthy Attorney-Richard C. Sughrue et al.

[57] ABSTRACT An anomalous dispersion glass having an Abbes number (vd) of 58-68 and a partial dispersion ratio (Phg) of 04425-04650, produced by adding 0.3-7.0 wt. parts of Ce0 and 0-2 wt. parts of Sb O to 100 wt. parts of phosphate glass which is composed of P 0 40-70 wt. percent, 8 0,, l-2l wt. percent, AI O l-8 wt. percent, B O +Al O 2-24 wt. percent, 8:10 8-42 wt. percent, ZnO 0-9 wt. percent, MgO 0-7 wt. percent, CaO 0-7 wt. percent, SrO O-ll wt. percent, La O O-7 wt. percent, where BaO+MgO+ZnO+SrO+CaO+La O are 15-52 wt. percent.

2 Claims, 1 Drawing Figure .PATENTEDJAHISIW --3.785.835

Phg

ANOMALOUS DISPERSION GLASS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an anomalous dispersion glass suitable for producing a superachromatic lens assembly.

2. Description of the Prior Art In order to design a superachromatic lens assembly, the chomatic aberration between 2 lights having mutually different wavelengths must be removed, and the residual chromatic aberration or the secondary spectrum must be minimized on a wide wavelength range. This secondary spectrum, however, cannot be minimized on a wide wavelength spectrum range by using only normal dispersion glass where the relationship between the Abbes number (vd) and the partial dispersion ratio (Phg) on the gh lines is linear. Therefore, a special glass having a partial dispersion ratio different from that of a normal dispersion glass, i.e., an anomalous dispersion glass having a non-linear relationship between the (vd) value and the (Phg) value, is required for producing a superachromatic lens assembly.

Generally, an anomalous dispersion glass having an anomalous dispersion property in the zone near the ultraviolet range is required, taking the kind of photosensitive material, the refractive index of the dispersion and the light wavelength sensitivity of the photoelectric tube into consideration. However, such an anomalous dispersion glass must have an Abbes number as high as possible in order to simultaneously minimize spherical aberration and chromatic aberration. Generally, the partial dispersing ratio describing these properties is shown approximately by 11g T'F/YIF 'ncmh ngl-qF no, or 1 1' mph/11F 110. The 11h w g/11F 1 c value is adopted as an indication of the anomalous dispersion property in this disclosure.

A conventional anomalous dispersion glass containing 'IiO has a high Abbes number but is unstable due to the influence of the TiO Much empirical experimentation has been carried out to obtain an anomalous dispersion glass which is stable and has a high Abbes number, and a favorable anomalous dispersion glass was found to be produced by adding CeO which has a strong absorption intensity in the ultraviolet ray zone near the visible light zone, to a phosphate glass. The phosphate glass, however, is tinged yellow by the Ce ion, and therefore this anomolous dispersion glass cannot be put to practical use.

SUMMARY OF THE INVENTION This invention provides an improved anomalous dispersion glass having an high Abbes number and anomalous dispersion property in the short wave light zone, which has good stability, good melting property and durability against chemical attack.

The anomalous dispersion glass according to this invention is produced by adding both 0.37.0 wt. parts of CeO and up to 2 wt. parts, e.g., -2 wt. parts of Sb O to I00 wt. parts of phosphate glass composed of P 0, 40-70 wt. percent, B 0 1-2I wt. percent, A1 0 1-8 wt. percent, B O +AI O 2-24 wt. percent, BaO 8-42 wt. percent. ZnO 0-9 wt. percent, MgO 0-7 wt. percent, CaO 0-7 wt. percent, SrO 0ll wt. percent, La o 0-7 wt. percent, and BaO+MgO+ZnO+SrO+CaO+La O -52 wt. percent, and has an Abbes number of 5868, and Phg value of O.44250.4650.

The drawing is a plot of the Abbes number versus partial dispersion ratio for glasses of this invention and the prior art.

DETAILED DESCRIPTION OF THE INVENTION As the P 0 which is the primary component of the phosphate glass, exhibits an absorption in the short wavelength zone apart from the visual light zone, the dispersion curve of the refractive index vs the wavelength in the visual light zone is gentle and the Abbe s number can be increased. In the case that the P 0 content is reduced below 40 percent, the Abbes number becomes too low, whereas in the case that the P 0 content exceeds percent, the stability of the glass is worsened.

CeO is decomposed into Ce and Ce ions in the glass, and both ions exhibit a strong absorption intensity in the ultraviolet ray zone near the visual light zone. Accordingly, the addition of the Geo, influences the dispersion curve, but this influence is restricted to the narrow range of a relatively short wave zone (about 250-450 mp.) by suitably selecting the CeO content, and the CeO scarcely effects the visual light zone near the C line and the F line. Therefore, the addition of Ce0 imparts a favorable anomalous dispersion property to the glass to provide relatively a large dispersion property in the ultraviolet ray zone and does not reduce the Abbes number. The effect of CeO in imparting a good anomalous dispersion property to the glass is similar to that of known TiO but CeO is not detrimental to the stability of the glass as is TiO This permits one to add considerable amounts of CeO to the phosphate glass composition. However, a glass containing less than 50 percent phosphate is readily and strongly colored yellow by adding only 0.5 percent of CeO a detriment due to the Ce ions. In order to apply such a CeO containing phosphate glass to practical use, the Ce ions must be reduced into Ce ions. Although a phosphate glass containing P 0 as the primary component is more acidic than other glasses, the yellow coloring due to Ce ions cannot be prevented. Sb O which is known as an oxidizer in the presence of nitrate, serves as a reducing agent for ions having an high oxidation-reduction potential. Thus the yellow coloring of the phosphate glass due to the Ce ion can be prevented by adding a small amount of Sb O to the phosphate glass. The amount of Sb O added to the glass may be as low as possible to prevent the yellow coloring. The addition of Sb O has no effect on the devitrification and chemical durability of the glass, and is effective to improve the stability of some special glass compositions.

If the Ce0 content is reduced below 0.3 percent, the anomalous dispersion property is not observed in the resulting glass. On the other hand, if the CeO content exceeds 7.0 percent the Abbes number becomes low and the yellow coloring due to Ce ion is difficult to erase. The yellow coloring of the glass due to the CeO addition becomes stronger as the amount of CeO increases and the amount of P 0 decreases. The amount of Sb O to be added to the glass is restricted below 2.0 percent so as to not decrease the Abbes number.

Since a glass containing solely P 0 as the glass forming component has a narrow vitrification range, poor stability and inferior chemical durability, both B and Al O are added to the glass composition. The amount of B 0 and A1 0 to be added to the glass are l-2l percent and l-8 percent, respectively. The sum M203 2.0 4.0 B 0 +A| o 5.0 10.0

ZnO 0.0 8.0

of B 0 and Al- O ranges from 2-24 percent. 5 M o 0 Oxides of alkaline earth metals, such as BaO, MgO, CaO 0.0 6.0 ZnO, CaO, SrO and La o are favorable glass modifi- S O 0.0 10,0 ers for the glass of this invention. 8-42 percent of BaO La O 0.0 6.0 improves the stability of the glass 0-7 percent of MgO BaO+ZnO+MgO+CaO+SrO+La O 30.0 51.0 also improves the stability of the glass together with the Some examples of this invention will be described other alkaline earth metal oxides. 0-9 percent f Zn with reference to Table 1) showing the composition of improves both stability and chemical durability. 0-7 each of the glass specimens; Table (2) showing several percent of CaO improves durability of the glass against physical properties of the glass specimens listed in chemicals. 0-ll percent of SrO is effective to improve Table (l); and the drawing which shows the relationthe stability of the glass in the case that it contains a re ll5 hi b t th Abb number (yd) f a normal di atively Small amount of 2 5- Percent of z a persion glass and the partial dispersion ratio (Phg) improves the resistance of the glass to chemicals. The thereof, and also the relationship between the Abbes sum of the amounts of these modifiers is preferably in number (vd) of the anomalous dispersion glass of this the range of from percent to 52 percent. invention and the practical dispersion ratio (Phg) Preferred ranges for the components of the glass thereof. composition of this invention are as follows: In the drawing, a line (A) shows the relationship between vd and Phg for the normal dispersion glass, 2 WL P8115 whereas the dots show the relationship for the anomaz a lous dispersion glass specimens according to this inven- P 0 43.0 65.0 wt. percent tion. The numerals on each dot correspond to the spec- B O 1.5 9.0 imen number in the tables.

" TABLE 1 specimen P,O5 8,0 AIZOJ BaO ZnO MgO CaO SrO La o, CeO, Sb,O No.

1 65.0 1.5 3.5 14.0 4.0 6.0 6.0 0 o 1.0 0 2 65.0 1.5 3.5 14.0 4.0 6.0 6.0 0 0 2.1 0.2 3 65.0 1.5 3.5 14.0 4.0 6.0 6.0 0 0 4.2 0.8 4 65.0 1.5 3.5 14.0 4.0 6.0 6.0 0 0 5.1 1.0 5 65.0 1.5 3.5 14.0 4.0 6.0 6.0 0 0 6.3 1.2 6 55.0 1.5 3.5 30.0 8.0 2.0 0 0 0 1.0 0 7 55.0 1.5 3.5 30.0 8.0 2.0 0 0 0 2.1 0.7 8 55.0 1.5 3.5 30.0 8.0 2.0 0 0 0 5.2 1.5 9 46.0 7.0 2.0 41.0 0 0 0 o 4.0 0.5 0.2 10 46.0 7.0 2.0 41.0 0 0 0 0 4.0 1.0 0.2 11 46.0 7.0 2.0 41.0 0 0 0 0 4.0 5.2 1.8 12 43.0 4.0 2.0 33.9 5.6 0 0 9.5 2.0 0.5 0.1 13 43.0 4.0 2.0 33.9 5.6 0 0 9.5 2.0 1.0 0.2 14 47.5 20.0 2.5 14.0 4.0 6.0 6.0 0 0 0.5 0 15 70.0 3.0 7.0 9.0 5.5 5.5 0 0 0 0.5 0 16 46.0 7.0 2.0 39.0 0 0 0 o 6.0 1.0 0.2 (wt.%)

*7 a Table 2 specimen and vd Phg Lt("C)' Da No.

1 1.54964 66.22 0.4432 850 3rd class 2 1.55377 65.90 0.4458 905 3 156203 64.79 0.4490 920 4 1.56402 64.18 0.4485 932 5 1.56682 63.75 0.4479 815 6 1.57425 65.23 0.4459 820 7 1.57672 63.74 0.4513 850 8 1.58549 62.38 0.4496 870 9 1.59089 65.50 0.4483 950 41h class 10 1.60096 64.55 0.4477 940 11 1.60554 62.36 0.4503 940 12 1.59324 64.98 0.4484 910 3rd 61m 13 1.60409 63.72 0.4483 910 14 158484 58.95 (1.4623 905 3rd Ch! 15 154102 64.12 0.4455 890 4111 (3'35; 16 1.60150 64.31 0.4573 958 Da is the durability ofthe 64.3l

Grade Weight loss(%) by acidic attack ls! class 0.2] 0.35 2nd class 0.36 0.65 3rd class 0.66 1.20 4th class l.2l 2.20 5th class 2 2.21

These glass specimens were prepared by blending the orthophosphoric acid, alkaline earth metal metaphosphates, and other carbonates, etc. in the amounts required for making the indicated composition above melting the composition at a temperature of from l,280 to l,330C for longer than about 30 minutes, usually for a period of less than 2 hours, stirring and clarifying the molten glass and casting the molten glass followed by gradual cooling.

It is apparent from the above examples that the anomalous dispersion glass of this invention has a high Abbes number (greater than 58) as compared to a conventional Ti-flint glass having a low Abbes number (ud value), i.e., less than 50, has a high partial dispersion ratio in the short wavelength ray zone, a low liquid phase temperature (below 950C), a favorable vitrification stability, a high durability against chemical attack and good light permeability.

While this invention has been described with reference to particular embodiments thereof, it will be understood that the numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention.

Therefore, the appended claims are intended to cover all such equivalent variations as coming within the true spirit and scope of the invention.

What is claimed is: 1

1. An anomalous dispersion glass produced by adding both 0.3-7.0 wt. parts of CeO and up to 2 wt. parts of Sb O to wt. parts of a phosphate glass which is composed of P 0 40-70 wt. percent, B 0 l-2l wt. percent, A1 0 1-8 wt. percent, B O;,+Al 0 2-24 wt. percent, BaO 8-42 wt. percent, ZnO 0-9 wt. percent, MgO 0-7 wt. percent, CaO 0-7 wt. percent, SrO O-l 1 wt. percent, La O 0-7 wt. percent, and BaO+MgO+ZnO+SrO-lCaO-l-La O 15-52 wt. percent.

2. The anomalous dispersion glass of claim 1, wherein said CeO ranges from 0.5 to 6.0 wt. parts and said Sb O ranges from 0.2 to 1.5 wt. parts and wherein said phosphate glass is composed of P 0 43-65 wt. percent, B 0 1.5-9.0 wt. percent, Al O 2.0-4.0 wt. percent, B,O +AI O 5.0-l0.0 wt. percent, B'aO 13.0-40.0 wt. percent, ZnO 0-8.0 wt. percent, MgO 06.0 wt. percent, CaO 06.0 wt. percent. SrO 0-l0.0 wt. percent, La O 06.0 wt. percent and BaO+MgO+ZnO+SrO+CaO+La O 30.0-51.0 wt. percent. 

2. The anomalous dispersion glass of claim 1, wherein said CeO2 ranges from 0.5 to 6.0 wt. parts and said Sb2O3 ranges from 0.2 to 1.5 wt. parts and wherein said phosphate glass is composed of P2O5 43-65 wt. percent, B2O3 1.5-9.0 wt. percent, Al2O3 2.0-4.0 wt. percent, B2O3+Al2O3 5.0-10.0 wt. percent, BaO 13.0-40.0 wt. percent, ZnO 0-8.0 wt. percent, MgO 0-6.0 wt. percent, CaO 0-6.0 wt. percent. SrO 0-10.0 wt. percent, La2O3 0-6.0 wt. percent and BaO+MgO+ZnO+SrO+CaO+La2O3 30.0-51.0 wt. percent. 